This invention relates to a proximity detector, and more particularly to a self-balancing capacitance bridge type proximity detector in which the bridge is automatically rebalanced when a metallic object which is to be detected unbalances the bridge network.
Proximity detectors have been utilized in a wide variety of applications, ranging from the more simple applications of counting piece parts for controlling manufacturing and packaging processes to the more difficult applications of counting turns of wire being wound on a core. The latter application of counting the number of turns of wire wound on a core by a winding machine is considered a more difficult counting problem due to the speed at which the winding machine operates and the diameter of the wire to be counted, which may be very fine. One approach to this problem is described in U.S. Pat. No. 3,226,531, which utilizes an impedance bridge which is unbalanced upon an approach of a strand of wire, generating a signal which is counted. The problem with this approach is that the impedance bridge must be initially manually balanced. However, the impedance bridge is temperature sensitive, and time unstable, so that it becomes unbalanced even in the absence of a turn of wire which it is designed to detect, thereby requiring an operator to continually check and rebalance the bridge for it to function properly. Accordingly the aforesaid device is subject to error, and requires periodic surveillance to insure that the bridge network is functioning properly.
It is an object of the present invention to provide a new and improved proximity detector which is automatically self-balancing.
A further object of this invention is to provide a new and improved proximity detector which is capable of operating accurately and at high speeds, and without operator intervention.
Still another object of this invention is to provide a new and improved proximity detector which is simple in operation and stable in operation with changes in temperature.